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    <title>Document</title>

    <script>
        //Boolean有两个固定的值，true和false
        var flag1 = true;
        var flag2 = false;
        console.log(flag1);
        console.log(flag2);

        var flag3;  //默认值是：undifine
        console.log(flag3 + 'aabbcc');
        console.log(flag3 + 1); //NaN

        console.log(true+1);//2  true对应的数字是1
        console.log(false+1);//1  false对应的数字是0
    
    </script>
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